There will be completely free updates to the game over time after the release. Planned features include the option for customizable playthroughs, although Achievements are unlocked. These settings include things like permanent Night, HAPPY + RISK, and much more.
An optional DLC is planned to be released sometime after the customizable modes, and it will feature a much vaster postgame that expands on side characters, the world, and the fate of the characters after the true endings. An additional, final ending will also be available, alongside more features to be revealed!